Evaluating material properties effect on residual insecticides for stored product insect control

Food processing and storage warehouses are complex structures composed of unique machinery, building materials, size, and design. Surface treatments of residual insects inside food processing and storage warehouses can be used to prevent insects from infesting new products, limiting population growth, and translocation within a facility. However, the porosity of materials, pH, and chemical formulation of insecticide can impact efficacy on stored product insects. Our study investigated how metal, concrete, and wood affected two different insecticide formulations containing the active ingredients Diacon®IGR Plus (active ingredients (a.i.) deltamethrin + methoprene) and Gravista™ (a.i. deltamethrin + methoprene + PBO) on Trogoderma variabile Ballion, warehouse beetle, and Trogoderma inclusum LeConte, larger cabinet beetle, adults. Bioassay arenas were created for each material on the bottom of a 62 cm2 Petri dish, and the insecticides were applied according to the label rates for each insecticide. Ten adult beetles were added to arenas along with ~500 mg of diet, and observed for live and dead adults after 1, 2, 3, and 4 d of exposure. As the length of exposure on the treated surfaces increased, mortality increased for both species. Mortality was highest on the metal surface for both species ranging from 78 – 94% among the two formulations compared to concrete surfaces which had mortalities ranging from 3 – 10% after 4 d of exposure. Therefore, determining where surface treatments are applied is critical for predicting the initial impact on adult Trogoderma spp. and potential length the insecticide is effective before re-application.